IMHO, the person responsible (your friend) should pay for the phone. Also, getting people to pay for things they broke can be pretty frustrating from my experience. Even if they intend to pay you back, it can sometimes take approximately forever for them to pay you back. You can usually tell these types of people from their track record.
Bottom line, don't get bent out of shape cause it's not worth it and if the person takes longer than a couple weeks to pay you back, just buy the phone yourself, make a mental note and don't lend that person any money or anything of value until he pays you back.
Unfortuantely, I've been in your situation a couple times and learned a few things about some of my friends. I still chill with them and they're still good freinds but I don't lend them ANYTHING anymore.
Here's hoping the guy pays you back and you have better luck than I did.